Electrodes including polyacrylate binders and methods of making and using the same

ABSTRACT

Provided is an electrode composition comprising a powdered material capable of undergoing lithiation and delithiation, and a non-elastomeric binder comprising lithium polyacrylate, along with methods of making and using the same, as well as electrochemical cells incorporating the same.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 11/671,601, filed Feb.6, 2007, now allowed, the disclosure of which is incorporated byreference in its entirety herein.

FIELD OF THE INVENTION

This invention relates to electrode binders for electrochemical cellsand to electrodes containing such binders.

BACKGROUND

Powdered alloys of main group elements and conductive powders such ascarbon black have been used to make electrodes for lithium-ion cells ina process that involves mixing the powdered active ingredients with apolymeric binder such as polyvinylidene fluoride. The mixed ingredientsare prepared as a dispersion in a solvent for the polymeric binder, andcoated onto a metal foil substrate, or current collector. The resultingcomposite electrode contains the powdered active ingredient in thebinder, adhered to the metal substrate.

Many polymers such as polyvinylidene fluoride, aromatic and aliphaticpolyimides and polyacrylates have been used as binders for metal andgraphite based lithium-ion cell electrodes. However, the first cycleirreversible capacity loss in the resulting cells can be unacceptablylarge, e.g., as large as 300 mAh/g or more for an electrode based on apowdered metal material.

Secondary electrochemical cells, such as lithium-ion cells, are capableof being reversibly charged and discharged multiple times. In the caseof lithium-ion batteries, the charging and the discharging of thelithium-ion electrochemical cells are accomplished by lithiating anddelithiating the cell electrodes. When lithium-ion cells areconstructed, they usually contain excess lithium-ions in the positiveelectrode and no lithium-ions in the negative electrode. During theinitial cycling reaction of the cells (charging), lithium transfers fromthe positive electrode to the negative electrode until the negativeelectrode has reached its capacity of absorbing lithium-ions. Upon thefirst discharge, the lithium-ions migrate from the lithiated negativeelectrode back to the positive electrode. Typically, after the firstcharging not all of the lithium-ions in the negative electrode are ableto migrate out of the negative electrode. This results in what is knownas irreversible loss in the capacity of the cell. Loss in the capacityof a cell from additional cycling (after the first cycle) is calledcapacity fade. This can be for a variety of reasons including changes inthe morphology of the active electrode material upon repeated cycling, abuildup of insulating layers on the active electrode material uponrepeated cycling or other reasons. A desirable lithium-ion cell is onethat has low irreversible capacity loss after the initial cycling, andhas low capacity loss (fade) after multiple cycles.

SUMMARY

In view of the foregoing, we recognize that there is a need forelectrodes that undergo reduced first cycle capacity loss (irreversiblecapacity loss) and reduced capacity fade.

In one aspect, this invention provides an electrode composition thatcomprises a powdered material capable of undergoing lithiation anddelithiation. In addition, the electrode composition includes anon-elastomeric binder that includes lithium polyacrylate.

In another aspect, this invention provides an electrochemical cell thatcomprises a positive electrode, a negative electrode, and anelectrolyte. The negative electrode, the positive electrode, or bothelectrodes include a powdered material capable of undergoing lithiationand delithiation and a non-elastomeric binder that includes lithiumpolyacrylate.

In yet a further aspect, this invention provides a method of making anelectrochemical cell electrode that includes providing a currentcollector, providing a powdered material capable of undergoinglithiation and delithiation, and applying to the current collector acoating that includes the powdered material and lithium polyacrylate.

The use of lithium polyacrylate as a binder provides reducedirreversible capacity and fade. The irreversible first cycle capacityloss in these electrodes can be significantly decreased by forming theelectrode using a lithium polyacrylate binder. Such a binder (which canbe prepared by neutralizing poly(acrylic acid) with lithium hydroxide)can be used to prepare electrodes and cells that experience decreasedfirst cycle irreversible capacity loss compared to electrodes or cellsmade with conventional polymeric binders.

The disclosed electrodes containing lithium polyacrylate binders canimprove cycle life in rechargeable lithium-ion cells employingelectrodes based on small particle alloy powders. The disclosed binderscan also allow fabrication of rechargeable lithium-ion cells havingimproved capacities or employing novel alloy powders.

In this application:

the terms “a”, “an”, and “the” are used interchangeably with “at leastone” to mean one or more of the elements being described;

the term “metal” refers to both metals and to metalloids such as siliconand germanium, whether in an elemental or ionic state;

the term “alloy” refers to a mixture of two or more metals;

the terms “lithiate” and “lithiation” refer to a process for addinglithium to an electrode material;

the terms “delithiate” and “delithiation” refer to a process forremoving lithium from an electrode material;

the term “active” refers to a material that can undergo lithiation anddelithiation;

the terms “charge” and “charging” refer to a process for providingelectrochemical energy to a cell;

the terms “discharge” and “discharging” refer to a process for removingelectrochemical energy from a cell, e.g., when using the cell to performdesired work;

the phrase “positive electrode” refers to an electrode (often called acathode) where electrochemical reduction and lithiation occurs during adischarging process; and

the phrase “negative electrode” refers to an electrode (often called ananode) where electrochemical oxidation and delithiation occurs during adischarging process.

Unless the context clearly requires otherwise, the terms “aliphatic”,“cycloaliphatic” and “aromatic” include substituted and unsubstitutedmoieties containing only carbon and hydrogen, moieties that containcarbon, hydrogen and other atoms (e.g., nitrogen or oxygen ring atoms),and moieties that are substituted with atoms or groups that may containcarbon, hydrogen or other atoms (e.g., halogen atoms, alkyl groups,ester groups, ether groups, amide groups, hydroxyl groups or aminegroups).

DETAILED DESCRIPTION

All numbers are herein assumed to be modified by the term “about”. Therecitation of numerical ranges by endpoints includes all numberssubsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3,3.80, 4, and 5).

Electrode compositions according to the present invention may be used innegative or positive electrodes. A variety of powdered materials can beemployed to make the electrode compositions. Exemplary powderedmaterials can for example contain silicon, silver, lithium, tin,bismuth, lead, antimony, germanium, zinc, gold, platinum, palladium,arsenic, aluminum, gallium, indium, thallium, molybdenum, niobium,tungsten, tantalum, iron, copper, titanium, vanadium, chromium, nickel,cobalt, zirconium, yttrium, a lanthanide, an actinide or an alloycontaining any of the foregoing metals or metalloids and other powderedactive metals and metalloids that will be familiar to those skilled inthe art. Graphitic carbon powder can also be used to make the disclosedelectrode compositions.

Exemplary powders can have a maximum length in one dimension that is nogreater than 60 μm, no greater than 40 μm, or no greater than 20 μm, oreven smaller. The powders can, for example, have a maximum particlediameter that is submicron, at least 1 μm, at least 2 μm, at least 5 μm,or at least 10 μm or even larger. For example, suitable powders oftenhave a maximum dimension of 1 to 60 μm, 10 to 60 μm, 20 to 60 μm, 40 to60 μm, 1 to 40 μm, 2 to 40 μm, 10 to 40 μm, 5 to 20 μm, or 10 to 20 μm.The powdered materials can contain optional matrix formers within powderparticles. Each phase originally present in the particle (i.e., before afirst lithiation) can be in contact with the other phases in theparticle. For example, in particles based on a silicon:copper:silveralloy, a silicon phase can be in contact with both a copper silicidephase and a silver or silver alloy phase.

Each phase in a particle can for example have a grain size less than 500Å, less than 400 Å, less than 300 Å, less than 200 Å, less than 150 Å,or even smaller.

Exemplary silicon-containing powdered materials useful in this inventioninclude the silicon alloys wherein the powdered material comprises fromabout 65 to about 85 mole percent silicon, from about 5 to about 12 molepercent iron, from about to about 12 mole percent titanium, and fromabout 5 to about 12 mole percent carbon. Additional examples of usefulsilicon alloys include compositions that include silicon, copper, andsilver or silver alloy such as those discussed in U.S. Pat. Appl. Publ.No. 2006/0046144 A1 (Obrovac et al); multiphase, silicon-containingelectrodes such as those discussed in U.S. Pat. No. 7,498,100(Christensen et al); silicon alloys that contain tin, indium and alanthanide, actinide element or yttrium such as those described in U.S.Pat. Publ. Nos. 2007/0020521, 2007/0020522, and 2007/0020528 (all toObrovac et al.) filed Mar. 23, 2006; amorphous alloys having a highsilicon content such as those discussed in U.S. Pat. No. 7,732,955(Christensen et al.); and other powdered materials used for negativeelectrodes such as those discussed in U.S. Pat. Publ. No. 2007/0269718(Krause et al.) and PCT Publ. No. WO 2007/044315 (Krause et al.). Eachof the foregoing references is incorporated herein in its entirety.

Other useful exemplary powdered materials for making positive electrodesof the invention include lithium alloys such as Li_(4/3)Ti_(5/3)O₄,LiV₃O₈, LiV₂O₅, LiCo_(0.2)Ni_(0.8)O₂, LiNiO₂, LiFePO₄, LiMnPO₄, LiCoPO₄,LiMn₂O₄, and LiCoO₂; lithium atoms intercalated within a lithiumtransition metal oxide such as lithium cobalt dioxide, lithium nickeldioxide, and lithium manganese dioxide; the lithium alloy compositionsthat include mixed metal oxides of cobalt, manganese, and nickel such asthose described in U.S. Pat. Nos. 6,964,828 and 7,078128 (Lu et al);6,203,944 (Turner); and 6,680,145 B2 (Obrovac et al.).

Exemplary powdered materials useful for making negative electrodes ofhis invention include U.S. Pat. No. 6,699,336 B2 (Turner et al.); U.S.Pat. Appl. Publ. No. 2003/0211390 A1 (Dahn et al.); U.S. Pat. Nos.6,255,017 B1 (Turner) and 6,436,578 B2 (Turner et al.); graphitic carbonthat exists in forms such as powders, flakes, fibers or spheres (e.g.,mesocarbon microbeads (MCMB)); combinations thereof and other powderedmaterials that will be familiar to those skilled in the art. Each of theforegoing references is incorporated herein in its entirety.

Powdered alloy particles may include a conductive coating. For example,a particle that contains silicon, copper, and silver or a silver alloycan be coated with a layer of conducting material (e.g., with the alloycomposition in the particle core and the conductive material in theparticle shell). Suitable conductive materials include, for example,carbon, copper, silver, or nickel.

Exemplary powdered alloy materials can be prepared by any known means,for example, by physically mixing and then milling the various precursorcomponents to the alloys. The mixing can be by simple blending or byusing a melt spinning process. According to this process, ingotscontaining the alloy composition can be melted in a radio frequencyfield and then ejected through a nozzle onto a surface of a rotatingwheel (e.g., a copper wheel). Because the surface temperature of therotating wheel is substantially lower than the temperature of the meltedalloy, contact with the surface of the rotating wheel quenches the melt.Quenching minimizes the formation of large crystallites that can bedetrimental to electrode performance. When conductive coatings areemployed, they can be formed using techniques such as electroplating,chemical vapor deposition, vacuum evaporation or sputtering. Suitablemilling can be done by using various techniques such as vertical ballmilling, horizontal ball milling or other milling techniques known tothose skilled in the art.

The electrode composition can contain additives such as will be familiarto those skilled in the art. The electrode composition can include anelectrically conductive diluent to facilitate electron transfer from thepowdered material to a current collector. Electrically conductivediluents include, but are not limited to, carbon (e.g., carbon black fornegative electrodes and carbon black, flake graphite and the like forpositive electrodes), metal, metal nitrides, metal carbides, metalsilicides, and metal borides. Representative electrically conductivecarbon diluents include carbon blacks such as SUPER P and SUPER S carbonblacks (both from MMM Carbon, Belgium), SHAWANIGAN BLACK (ChevronChemical Co., Houston, Tex.), acetylene black, furnace black, lampblack, graphite, carbon fibers and combinations thereof.

The electrode composition can include an adhesion promoter that promotesadhesion of the powdered material or electrically conductive diluent tothe binder. The combination of an adhesion promoter and binder can helpthe electrode composition better accommodate volume changes that canoccur in the powdered material during repeated lithiation/delithiationcycles. The disclosed binders can offer sufficiently good adhesion tometals and alloys so that addition of an adhesion promoter may not beneeded. If used, an adhesion promoter can be made a part of the lithiumpolyacrylate binder (e.g., in the form of an added functional group),can be a coating on the powdered material, can be added to theelectrically conductive diluent, or can be a combination of suchmeasures. Examples of adhesion promoters include silanes, titanates, andphosphonates as described in U.S. Pat. Appl. Publ. No. 2004/0058240 A1(Christensen), the disclosure of which is incorporated herein byreference.

The binders of this invention contain lithium polyacrylate. Lithiumpolyacrylate can be made from poly(acrylic acid) that is neutralizedwith lithium hydroxide. In this application, poly(acrylic acid) includesany polymer or copolymer of acrylic acid or methacrylic acid or theirderivatives where at least about 50 mole %, at least about 60 mole %, atleast about 70 mole %, at least about 80 mole %, or at least about 90mole % of the copolymer is made using acrylic acid or methacrylic acid.Useful monomers that can be used to form these copolymers include, forexample, alkyl esters of acrylic or methacrylic acid that have alkylgroups with 1-12 carbon atoms (branched or unbranched), acrylonitriles,acrylamides, N-alkyl acrylamides, N,N-dialkylacrylamides,hydroxyalkylacrylates, and the like. Of particular interest are polymersor copolymers of acrylic acid or methacrylic acid that are watersoluble—especially after neutralization or partial neutralization. Watersolubility is typically a function of the molecular weight of thepolymer or copolymer and/or the composition. Poly(acrylic acid) is verywater soluble and is preferred along with copolymers that containsignificant mole fractions of acrylic acid. Poly(methacrylic) acid isless water soluble—particularly at larger molecular weights.

Homopolymers and copolymers of acrylic and methacrylic acid that areuseful in this invention can have a molecular weight (M_(W)) of greaterthan about 10,000 grams/mole, greater than about 75,000 grams/mole, oreven greater than about 450,000 grams/mole or even higher. Thehomopolymers and copolymer that are useful in this invention have amolecular weight (M_(W))) of less than about 3,000,000 grams/mole, lessthan about 500,000 grams/mole, less than about 450,000 grams/mole oreven lower. Carboxylic acidic groups on the polymers or copolymers canbe neutralized by dissolving the polymers or copolymers in water oranother suitable solvent such as tetrahydrofuran, dimethylsulfoxide, N,N-dimethylformamide, or one or more other dipolar aprotic solvents thatare miscible with water. The carboxylic acid groups (acrylic acid ormethacrylic acid) on the polymers or copolymers can be titrated with anaqueous solution of lithium hydroxide. For example, a solution of 34%poly(acrylic acid) in water can be neutralized by titration with a 20%by weight solution of aqueous lithium hydroxide. Typically, 50% or more,60% or more, 70% or more, 80% or more, 90% or more, 100% or more, 107%or more of the carboxylic acid groups are lithiated (neutralized withlithium hydroxide) on a molar basis. When more than 100% of thecarboxylic acid groups have been neutralized this means that enoughlithium hydroxide has been added to the polymer or copolymer toneutralize all of the groups with an excess of lithium hydroxidepresent.

The binders of this invention may be blended with other polymericmaterials to make a blend of materials. This may be done, for example,to increase the adhesion, to provide enhanced conductivity, to changethe thermal properties or to affect other physical properties of thebinder. The binders of this invention, however, are non-elastomeric. Bynon-elastomeric it is meant that the binders do not contain substantialamounts of natural or synthetic rubber. Synthetic rubbers includestyrene-butadiene rubbers and latexes of styrene-butadiene rubbers. Forexample, the binders of this invention contain less than 20% by weight,less than 10% by weight, less than 5% by weight, less than 2% by weight,or even less of natural or synthetic rubber.

To make a positive or a negative electrode, the active powderedmaterial, any selected additives such as binders, conductive diluents,fillers, adhesion promoters, thickening agents for coating viscositymodification such as carboxymethylcellulose and other additives known bythose skilled in the art are mixed in a suitable coating solvent such aswater or N-methylpyrrolidinone (NMP) to form a coating dispersion orcoating mixture. The dispersion is mixed thoroughly and then applied toa foil current collector by any appropriate dispersion coating techniquesuch as knife coating, notched bar coating, dip coating, spray coating,electrospray coating, or gravure coating. The current collectors aretypically thin foils of conductive metals such as, for example, copper,aluminum, stainless steel, or nickel foil. The slurry is coated onto thecurrent collector foil and then allowed to dry in air followed usuallyby drying in a heated oven, typically at about 80° C. to about 300° C.for about an hour to remove all of the solvent.

A variety of electrolytes can be employed in the disclosed lithium-ioncell. Representative electrolytes contain one or more lithium salts anda charge-carrying medium in the form of a solid, liquid or gel.Exemplary lithium salts are stable in the electrochemical window andtemperature range (e.g. from about −30° C. to about 70° C.) within whichthe cell electrodes can operate, are soluble in the chosencharge-carrying media, and perform well in the chosen lithium-ion cell.Exemplary lithium salts include LiPF₆, LiBF₄, LiClO₄, lithiumbis(oxalato)borate, LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂, LiAsF₆, LiC(CF₃SO₂)₃,and combinations thereof. Exemplary charge-carrying media are stablewithout freezing or boiling in the electrochemical window andtemperature range within which the cell electrodes can operate, arecapable of solubilizing sufficient quantities of the lithium salt sothat a suitable quantity of charge can be transported from the positiveelectrode to the negative electrode, and perform well in the chosenlithium-ion cell. Exemplary solid charge carrying media includepolymeric media such as polyethylene oxide, polytetrafluoroethylene,polyvinylidene fluoride, fluorine-containing copolymers,polyacrylonitrile, combinations thereof and other solid media that willbe familiar to those skilled in the art. Exemplary liquid chargecarrying media include ethylene carbonate, propylene carbonate, dimethylcarbonate, diethyl carbonate, ethyl-methyl carbonate, butylenecarbonate, vinylene carbonate, fluoroethylene carbonate, fluoropropylenecarbonate, y-butylrolactone, methyl difluoroacetate, ethyldifluoroacetate, dimethoxyethane, diglyme (bis(2-methoxyethyl) ether),tetrahydrofuran, dioxolane, combinations thereof and other media thatwill be familiar to those skilled in the art. Exemplary charge carryingmedia gels include those described in U.S. Pat. Nos. 6,387,570 (Nakamuraet al.) and 6,780,544 (Noh). The charge carrying media solubilizingpower can be improved through addition of a suitable cosolvent.Exemplary cosolvents include aromatic materials compatible with Li-ioncells containing the chosen electrolyte. Representative cosolventsinclude toluene, sulfolane, dimethoxyethane, combinations thereof andother cosolvents that will be familiar to those skilled in the art. Theelectrolyte can include other additives that will familiar to thoseskilled in the art. For example, the electrolyte can contain a redoxchemical shuttle such as those described in U.S. Pat. Nos. 5,709,968(Shimizu), 5,763,119 (Adachi), 5,536,599 (Alamgir et al.), 5,858,573(Abraham et al.), 5,882,812 (Visco et al.), 6,004,698 (Richardson etal.), 6,045,952 (Kerr et al.), and 6,387,571 B1 (Lain et al.); and inU.S. Pat. Appl. Publ. Nos. 2005/0221168 A1, 2005/0221196 A1,2006/0263696 A1, and 2006/0263697 A1 (all to Dahn et al.).

Electrochemical cells of this invention are made by taking at least oneeach of a positive electrode and a negative electrode as described aboveand placing them in an electrolyte. Typically, a microporous separator,such as CELGARD 2400 microporous material, available from HoechstCelanese, Corp., Charlotte, N.C., is used to prevent the contact of thenegative electrode directly with the positive electrode. This isespecially important in coin cells such as, for example, 2325 coin cellsas known in the art.

Electrochemical cells made with the negative electrodes of thisinvention showed reduced irreversible capacity loss and less fade thansimilar cells containing negative electrodes with conventional binders.

The disclosed cells can be used in a variety of devices, includingportable computers, tablet displays, personal digital assistants, mobiletelephones, motorized devices (e.g., personal or household appliancesand vehicles), instruments, illumination devices (e.g., flashlights) andheating devices. One or more electrochemical cells of this invention canbe combined to provide battery pack. Further details regarding theconstruction and use of rechargeable lithium-ion cells and battery packswill be familiar to those skilled in the art.

The invention is further illustrated in the following illustrativeexamples, in which all parts and percentages are by weight percent (wt%) unless otherwise indicated.

EXAMPLES

Preparatory Example 1

Preparation of Si₇₀Fe₁₀Ti₁₀C₁₀ Alloy

Si₇₀Fe₁₀Ti₁₀ was prepared by melting silicon lumps (65.461 grams)(AlfaAesar/99.999%, Ward Hill, Mo.), iron pieces (18.596 grams) (AlfaAesar/99.97%) and titanium sponge (15.943 grams) (Alfa Aesar/99.7%) inan ARC furnace. The alloy ingot of Si₇₀Fe₁₀Ti₁₀ was broken into smallchinks and was treated in a hammer mill to produce alloy powderparticles of approximately 150 micrometers.

Si₇₀Fe₁₀Ti₁₀C₁₀ alloy was made from Si₇₀Fe₁₀Ti₁₀ alloy powder (describedabove) and graphite (TIMREX SFG44, TimCal Ltd., Bodio, Switzerland) byreactive ball milling in a high kinetic ball mill (SIMOLOYER, CM20-201m,Zoz GmbH, Wenden, Germany). A sample of 1.4423 kg of Si₇₀Fe₁₀Ti₁₀ alloypowder, 0.0577 kg graphite and 25 kg of 4.76 millimeter diameterchromium-steel balls were charged to the mill. The mill was operated for180 cycles where each cycle consisted of 45 seconds at 550 revolutionsper minutes (rpm) and then 15 seconds at 300 rpm. The total milling timewas 3 hours. The mill was cooled by chilled water during the milling.

Preparatory Example 2 Preparation of Lithium Polyacrylate

Lithium polyacrylate was made by adding an aqueous solution of lithiumhydroxide solution to an aqueous poly(acrylic acid) solution. Differentmolar ratios of lithium hydroxide and carboxylic acid groups were used.Typically a 20 wt % aqueous solution of lithium hydroxide and a 34 wt %aqueous solution of poly (acrylic acid) were used. De-ionized water wasadded to bring the final solution of lithium polyacrylate to 10 wt %solids. Poly(acrylic acid) of 100,000 (M_(W)) and 250,000 (M_(W)) wereobtained as aqueous solutions from Aldrich Chemicals, Milwaukee, Wis..Samples of 65% LiOH neutralized lithium polyacrylate, of both 100,000M_(W) and 250,000 M_(W) , were prepared by adding 185.56 grams ofde-ionized water and 60.41 grams of 20% lithium hydroxide solution and100 grams poly(acrylic acid) (PAA) solution (34 wt % in water). Theresults were 10% solids solutions of lithium polyacrylate which had been64% neutralized. The two samples were designated lithium (64%)polyacrylate PAA100k-64% Li salt and lithium (64%) polyacrylatePAA250k-64% Li salt.

Additional samples of 107% of neutralized lithium polyacrylate wereprepared using both the 100,000 M_(W) and the 250,000 M_(W) polymer byadding 149.01 grams of de-ionized water and 106.01 grams of 20% lithiumhydroxide solution to 100 grams poly(acrylic acid) solution (34 wt % inwater). The results were 10% solids solutions of lithium polyacrylatewith a 7 mole % excess of lithium hydroxide. The two samples weredesignated lithium (107%) polyacrylate PAA100k-107% Li Salt and lithium(107%) polyacrylate PAA250k-107% LI salt.

TABLE 1 Calculated Weight % of total, dried coating Example 1 2 3 4 5 67 8 9 10 Si₇₀Fe₁₀Ti₁₀C₁₀ 60 92 60 92 — — 92 — 5 47.5 65 wt %Si₇₀Fe₁₀Ti₁₀C₁₀: — — — — — 92 — — — — 35 wt % SLP30 MCMB 1028 32 — — — —— — — — — MCMB 6-28 — — — — — — — — 90 — SFG44 — 47.5 KETJEN Black 1.21.2 — — — — — — — — PAA100k-64% Li salt 6.8 6.8 — — — — — — — — SLP30 —— 32 — 95 — — 95 — — PAA100k-107% Li salt — — 8 8 5 — — — — —PAA250k-107% Li salt — — — — — 8 8 5 — — KYNAR 741 — — — — — — — — 5 5Die Gap for coating (μm) 125 75 125 75 125 75 75 75 250 250

Electrode Fabrication Example 1

KETJEN Black conductive carbon (0.024g) (Akzo Nobel Polymer ChemicalLLC, Chicago, Ill.) and PAA100k-64% Li salt (1.36 g of a 10% solidssolution in water, were mixed in a 45-mL stainless steel vessel usingfour 13 micrometer diameter tungsten carbide balls. The mixing wascarried out in a planetary micro mill (PULVERSETTE 7 Model; Fritsch,Germany) at a speed setting of 1 for 30 minutes. Then Si₇₀Fe₁₀Ti₁₀C₁₀powder (1.20 g), MCMB-1028 graphite (0.64 g) (MMM Carbon, Belgium) andde-ionized water (0.1 g) were added to the mill and the mixing wascontinued at a speed setting of 2 for 30 minutes. The resulting solutionwas coated onto a 13-micron thick Cu foil using a die with a 125 μm gap.The sample was then dried in a vacuum oven at 120° C. for 2 hours.

Example 2

An electrode based on the composition of Example 2 in Table 1 wasprepared by the procedure used for Example 1 except that only 1.84 gramsof Si₇₀Fe₁₀Ti₁₀C₁₀ powder was added to the milled conductive carbon andpolymer mixture. The milled coating solution was coated onto copper foilusing a 75 μm gap.

Example 3

An electrode based on the composition of Example 3 in Table 1 wasprepared by the procedure used for Example 1 except that Si₇₀Fe₁₀Ti₁₀C₁₀powder (1.20 g), SLP30-Graphite (0.64 g) (TIMREX SLP30, TimCal Ltd.,CH-6743 Bodio, Switzerland), de-ionized water (1.0 g) and PAA100k-107%Li salt (1.6 g of a 10% solids solution in water) were milled in asingle step at a speed setting of 2 for 30 minutes. The milled solutionwas spread onto the copper foil using a 3 μm gap.

Example 4

An electrode based on the composition of Example 4 of Table lwasprepared by the same procedure used for Example 3, except that only 0.2grams of de-ionized water was added. The milled solution was spread ontothe copper foil using a 3 mil gap.

Example 5

An electrode based on the composition of Example 5 of Table 1 wasprepared by the same procedure used for Example 3, except that 2.5 gramsof de-ionized water was used with the graphite and the poly(acrylicacid) in the milling step. The milled solution was spread onto thecopper foil using a 3 mil gap.

Examples 6 and 7

Electrodes based on the compositions of Example 6 and Example 7 of Table1 were prepared by the same procedure used for Example 4.

Example 8

An electrode based on the composition of Example 8 in Table 1 wasprepared by the same procedure used for Example 5.

Comparative Example 1

Graphite (1.00 gram) (MCMB, Grade 6-28, Osaka Gas Co. Osaka-Shi, Japan),Si₇₀Fe₁₀Ti₁₀C₁₀ (0.1 gram), polyvinylidene fluoride (KYNAR 741) solution(1.0 gram of a 10% by weight solution in N-methyl pyrrolidinone (NMP)),and NMP (2.5 grams) were mixed in planetary micro mill as described forExample 1. The mixture was coated and dried as in Example 1.

Comparative Example 2

Si₇₀Fe₁₀Ti₁₀C₁₀ powder (2.0 grams) and TIMREX SFG44 graphite (2.0 grams)were mixed in the micro mill used for Example 1 at a speed setting of 7for 30 minutes.

This mixture (1.90 grams), polyvinylidene fluoride (KYNAR 741) solution(1.0 grams) and NMP (3.0 grams) were mixed in the micro mill of Example1 at a speed setting of 2 for one hour. The mixture was coated and driedas in Example 1.

Test Cell Assembly

Disks (16-mm diameter) were cut from the electrode coatings for use in2325-button cells. Each 2325 cell contains a 18 mm diameter disk of Cuas a spacer (36-mil (900 μm) thick), an 18 mm diameter disk of the alloyelectrode, one 20 mm diameter microporous separator (CELGARD 2400;Separation Products, Hoechst Celanese Corp., Charlotte, N.C. 28273)), 18mm diameter lithium (0.38 mm thick lithium ribbon; Aldrich Chemicals,Milwaukee, Wis.) and an 18 mm diameter copper spacer (600 μm thick). Onehundred microliters of electrolyte solution (1M LiPF₆ in 90wt % ethylenecarbonate (EC): diethylene carbonate (DEC) (1:2 v/v) (Ferro Chemicals(Zachary, La.); 10 wt % fluoroethylene carbonate (FEC) (Fujian ChuangxinScience and Technology Development, LTP, Fujian, China)) were mixed andused as the electrolyte. The electrolyte mixture was dried overmolecular sieves (3A type) over 12 hrs. The coin cells were charged anddischarged from 0.005V to 0.90V with a constant current of 250 mA/g foralloy and alloy/graphite electrodes and with a constant current of 100mA/g for graphite electrodes. During charging, when the cell reached0.90V, the cell voltage was held constant and the charging continueduntil the current reached 10 mA/g. The cell was allowed to remain atopen circuit for fifteen minutes at the end of every half cycle.

The initial charge capacity of each cell was calculated from themeasured total milliamp-hours charged until the cell voltage reached0.005V. The cell was then discharged as described above. Theirreversible capacity loss (shown in Table 2) was calculated from thedifference between the initial charge capacity and the first dischargecapacity divided by the initial capacity times 100. The data in Table 2show that negative electrodes made using the binders of this inventionhave less irreversible capacity loss compared with electrodes made withpolyvinylidene fluoride binders.

TABLE 2 Initial Charge Capacity and Irreversible Capacity of Examples1-8 Initital Charge Capacity Irreversible Capacity (mAh/g ActiveMaterial) Loss (%) Example 1 No Data No Data Example 2 No Data No DataExample 3 982 10.0 Example 4 1339 10.4 Example 5 392 8.7 Example 6 9879.8 Example 7 1339 9.6 Example 8 397 8.3 Comparative 388 15.7 Example 1Comparative 819 19.3 Example 2

The discharge capacity after cycle 5 and after cycle 50 for each cell isprovided in Table 3. The data show that cells containing negativeelectrodes with binders of this invention have less fade after 50 cyclesthan those made with polyvinylene fluoride binders.

TABLE 3 Discharge Capacity at Cycle 5 and at Cycle 50 for Examples 1-8Discharge Capacity Discharge Capacity at Cycle 5 at Cycle 50 (mAh/gAlloy and (mAh/g Alloy and % Capacity Loss/ graphite) graphite) CycleExample 1 864  854 0.026 Example 2 1219 1179 0.073 Example 3 891  8621.072 Example 4 1190 1134 0.105 Example 5 363  362 0.006 Example 6 897 847 0.012 Example 7 1219 1138 0.144 Example 8 365  366 — Comparative311  289* 0.157 Example 1 Comparative 451  136 1.550 Example 2*Comparative Example 1 Discharge Capacity at Cycle 19

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications can bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

1. An electrode composition comprising: a powdered active materialcapable of undergoing lithiation and delithiation; and a non-elastomericbinder comprising lithium polyacrylate, wherein the powdered activematerial comprises a lithium metal oxide comprising at least one ofcobalt, manganese, and nickel.
 2. An electrode composition according toclaim 1, wherein the lithium metal oxide comprises cobalt, manganese andnickel.
 3. An electrode composition according to claim 1, wherein theamount of lithium polyacrylate is 5 or more weight percent of the weightof the total composition.
 4. An electrode composition according to claim1, wherein the powdered material further comprises iron, titanium, orvanadium.
 5. An electrode composition according to claim 1, wherein thepowdered material comprises lithium cobalt oxide.
 6. An electrochemicalcell comprising: a positive electrode; a negative electrode; and anelectrolyte, wherein the positive electrode comprises a non-elastomericbinder comprising lithium polyacrylate, and wherein the powdered activematerial comprises a lithium metal oxide comprising at least one ofcobalt, manganese, and nickel.
 7. An electrochemical cell according toclaim 6, wherein powdered active material comprises a lithium metaloxide comprising at least one of cobalt, manganese, and nickel.
 8. Anelectrochemical cell according to claim 6, wherein the amount of lithiumpolyacrylate in the non-elastomeric binder is 5 or more weight percentof the weight of the total composition.
 9. An electrochemical cellaccording to claim 6, wherein the powdered active material furthercomprises a material selected from iron, titanium, vanadium, andcombinations thereof.
 10. An electrochemical cell according to claim 6,wherein the cell further comprises a secondary electrochemical cell. 11.An electrochemical cell according to claim 6, wherein the negativeelectrode comprises a silicon alloy.
 12. An electrochemical cellaccording to claim 6, wherein the alloy further comprises iron,titanium, or vanadium.
 13. An electrochemical cell according to claim 6,wherein the negative electrode comprises graphitic carbon.
 14. A batterypack comprising at least electrochemical cell according to claim
 6. 15.A method of making an electrochemical cell electrode comprising:providing a current collector; providing a powdered active materialcapable of undergoing lithiation and delithiation; and applying to thecurrent collector a coating that comprises the powdered active materialand lithium polyacrylate, wherein the powdered active material comprisesa lithium metal oxide comprising at least one of cobalt, manganese, andnickel.
 16. A method of making an electrochemical cell electrodeaccording to claim 15, wherein powdered active material comprises alithium metal oxide comprising at least one of cobalt, manganese, andnickel.
 17. A method of making an electrochemical cell electrodeaccording to claim 15, wherein the amount of lithium polyacrylate in thenon-elastomeric binder is 5 or more weight percent of the weight of thetotal composition.
 18. A method of making an electrochemical cellelectrode according to claim 15, wherein the powdered active materialfurther comprises a material selected from iron, titanium, vanadium, andcombinations thereof
 19. A method of making an electrochemical cellelectrode according to claim 15, wherein applying the coating furthercomprises: mixing the powdered material with a solution of lithiumpolyacrylate to form a dispersion; milling the dispersion to form acoatable mixture; coating the mixture onto the current collector; anddrying the coated current collector.